The properties of optical waveguides such as optical fibers make them an ideal choice of medium for carrying signals in an ever-increasing number of applications. These properties include high bandwidth (signal carrying capacity), immunity to interference, absence of radiation, low loss, light weight and low bulk. Optical fiber is often used in conjunction with electrical cables for carrying power, in applications such as turrets, remotely operated vehicles for hazardous locations, and industrial workstations. In such applications the composite cable is winched or reeled, requiring a slip ring or rotary joint assembly at the reel, to permit the payout or retraction of cable while allowing continuous operation of the remote equipment.
Electrical slip rings for the copper wires carrying power are well established, and fiber optic rotary joints have more recently appeared. However the use of fiber optic rotary joints has been somewhat limited by their performance, a particular weakness being the need to occupy the central axis of rotation of the rotary joint. This is a severe limitation in many cases, where shafts must occupy the axis of rotation, such as web dryers, stacker-reclaimers, rotating stages, shipboard winches, and many other applications. In other cases, people must occupy the central axis, such as in medical scanners and armoured vehicles.
Signal quality problems with electrical slip rings in CT scanner systems have indicated a potential requirement for an off-axis rotary joint. X-ray discharge causes interference with electrical signals passing through electrical slip rings and data rates with such systems need improvement. Optical fibers would overcome most of the problems in such equipment.
In armoured vehicles there is a trend towards the use of fiber optics for voice, video and digital signals to replace the electrical systems, giving higher bandwidth, reduced bulk and weight and absence of interference or radiation. As the turret rotates relative to the vehicle body, a slip ring or rotary joint is required. This has traditionally been located on-axis, to take advantage of available technology. However, a rotary joint having a hollow bore or shaft area would provide significant benefits by permitting easier movement of personnel and ammunition along the central area of the turret.
Many industrial installations can benefit from the advantages of fiber optics if they can replace noise-prone electrical data/control systems. Those having a rotational interface include cranes, mining machines, tethered vehicles, pulp/web dryers, machining turrets and many others. In some cases the central axis must be occupied by a shaft or other objects, demanding that the rotary joint operate off-axis.